The ticking clock of Iran's nuclear threat

In this April 8, 2008 photo released by the Iranian President's Office, Iranian President Mahmoud Ahmadinejad, center, visits the Natanz Uranium Enrichment Facility some 200 miles south of the capital, Tehran, Iran.

Iran this weekend accused the CIA of masterminding the assassination of a nuclear scientist on the streets of Tehran this past Wednesday. The U.S. denies any involvement. Nevertheless, the clock is ticking in the Persian Gulf in what some fear could be a countdown to war. Our cover story is reported by national security correspondent David Martin:

The young Iranian nuclear scientist who was buried this weekend knew he was a target for assassination. He had a bodyguard. But they both were killed as they drove to work, by a motorcyclist who came alongside and clamped a magnetic bomb to their car.

"This recent killing has got to be a blow to the Iranian government. That bodyguard didn't do his job, and the Iranian government didn't do their job to protect these scientists," said former weapons inspector David Albright, who keeps tabs on Iran's nuclear scientists.

"What difference do you think it makes now that he is no longer part of the Iranian nuclear program?" asked Martin.

"I hate to say it so crudely, but he's replaceable," replied Albright.

He said there is no one - as far as anyone can tell - who is irreplacable.

Except possibly for Mohsen Fakhrizadeh, a mysterious figure who is believed to head their nuclear weapons program but has never been seen in public.

"Certainly intelligence agencies that are interested in assassination would have a high interest in killing him," said Albright.

The CIA would no doubt like to see him dead, but it is barred by an executive order from conducting assassinations, like the one last week.

"We were not involved in any way, in any way, with regards to the assassination that took place there," said Defense Secretary Leon Panetta, who used to run the Central Intelligence Agency. "I'm not sure who was involved, we have some ideas as to who might be involved, but we don't know exactly who was involved.

"But I can tell you one thing: The United States was not involved in that kind of effort. That's not what the United States does."

You don't have to be a former CIA director to have the idea that Israel - which views Iran's nuclear program as a threat to its very existence - was involved in that and other assassinations of Iranian scientists.

Albright estimates there are hundreds of, professionals at the top level of Iran's nuclear program.

"So in the past two years, three have been killed," said Martin. "What kind of impact is that?"

"Doesn't have much direct impact, I would say," Albright said.

It certainly has not stopped Iran from enriching uranium to higher levels of purity by running it through centrifuges. But according to Dennis Ross, who until recently was the Obama administration's point man on Iran, the enrichment program is way behind schedule.

"By their own measure, they should have been at 50,000 centrifuges operating, and there are about 8,000 installed. So that's dramatically short of where they would have been," he said.

That's due in part to something called Stuxnet, a computer virus that someone - perhaps the U.S., perhaps Israel - infiltrated into the systems that run the centrifuges, causing them to spin out of control and self-destruct.

Albright believes the Stuxnet attack set back Iran's nuclear efforts by about a year.

But now Iran says it's opened a new uranium enrichment plant - dug deep into a mountain - that will allow it to step up production.

"By the end of this year they are going to have about 250 kilos of this 20 percent enriched uranium, which is a matter of concern for the international community," said Olli Heinonen, who used to inspect Iran's centrifuges for the International Atomic Energy Agency.